The long-term objective of this project is to identify the structural component of LPS which enhances tumor resistance of mice. The anti-tumor effect of some endotoxins does not appear to be related to its toxic properties. Accordingly, we intend to isolate and identify those components of the complex LPS molecule which promote tumor resistance. The use of rough mutants of Salmonella minnesota whose chemical composition and structure have been extensively studied provide a valuable tool in the structure to function relationship of LPS. Their enzyme deficiencies are characterized by a partial or complete loss of the polysaccharide moiety of the O-antigens. Primary attention will focus on the chemical and biological differences between the S. minnesota R-5 and R-7 mutants. Physical, chemical and immunological methods will be applied to obtain homogeneous endotoxic fractions, and to identify chemical and structural components of these fractions. These characterized fractions will be tested for biological activity in tumor resistance using several animal tumor models. Fractions will also be tested for classical endotoxicity properties as well as biological properties.